Quiz Corner: Charles’ Law

David W. Spitzer

Increasing the temperature of a gas from 30 C to 60 C will increase its volume by approximately:

A. 0 percent (no volume change)
B. 5 percent
C. 10 percent
D. 50 percent
E. 100 percent

Commentary

For flow measurement purposes, Charles’ Law is often used to calculate the change in volume that occurs when temperature changes:

V / V₀ = T / T₀

where V is volume and T is the absolute temperature. In this application, T₀ is approximately 300 Kelvins (273+30) and T is approximately 330 Kelvins (273+60). The new volume is therefore approximately 1.1 times (330/300) times the old volume, so the new volume is about 10 percent greater than the old volume. Therefore, the correct answer is Answer C.

Additional complicating factors

Charles’ Law was used above assuming that the gas is ideal. If the gas is not ideal, other methods can be employed to account for non-linearity and pressure effects on density such as the Non-Ideal Gas Law, density tables, or other such techniques. In actual applications, remember that the composition of the gas can change and affect these calculations.

David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC offering engineering, seminars, strategic, marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. He has more than 35 years of experience and has written over 10 books and 250 articles about flow measurement, instrumentation and process control.

Mr. Spitzer can be reached at 845 623-1830 or spitzerandboyes.com. Click on the "Products" tab in the navigation menu to find his "Consumer Guides" to various flow and level measurement technologies.